Propeller simulating system for aircraft trainers



Sept. 6, 1960- R. H. GOODWIN PROPELLER SIMULATING SYSTEM FOR AIRCRAFT TRAINEJRS Original Filed July 22, 1954 5 Sheets-Sheet 2 /Laloa DALE! MAINE. REEYNE Zona M MJ [AL .4 RESYN E :4

INVENTQ RUEJEDE H. El] WIN dj ATTEIRNEY Sept. 6, 1960 R. H. GoDwlN PROPELLER SIMULATING SYSTEM FOR AIRCRAFT TRAINERS original Filed July 22, 1954 5 Sheets-Sheet 3 ma? i l fEFMTna gl@ cO 11i. 2550 INVENTOR. HIIIEIEDE H. EIDCIDWIN BY gc/LM/ Y HIE ATTDRNEY Sept. 6, 1960- R. H. GOODWIN 2,951,298

PROPELLER SIMULATING SYSTEM FOR ARCRAF'T TRAINERS FE- BY Sept. 6, 1960 R. H. GOODWIN 2,951,298

lROFELLER SIMULATING SYSTEM FOR AIRCRAFT TRAINERS Original Filed Ju1y722, 1954 5 Sheets-Sheet 5 RENNI: -EYNC- EU TTUN4 30 REEYNI: #P3 M +5 (dc) 2 an 5 l l INVENTOR. RESCUE H. EDDDWIN HIS ATTDRNEY United States arent() PROPELLER SMULATING SYSTEM FOR AIRCRAFT TRAINERS Roscoe H. Goodwin, Allendale, NJ., assignor to Curtiss- Wright Corporation, a corporation of Delaware Continuation of application Ser. No. 445,090, July 22, 1954. This application July 18, 1957, Ser. No.

v17 Claims. (Cl. 35-12) designation) and the DC-6 (commercial designation) include a well-known propeller of the variable pitch constant speed type having hydraulically operated means which determine propeller pitch according to the setting of an engine governor. Electrical control means set the governor of each engine according to a preselected r.p.m. and the pitch of the propeller is determined accordingly. The r.p.m. and propeller pitch for 'the various engines of the aircraft may be changed simultaneously by means of a master control lever, or alternatively may be regu lated separately by toggling switches.

An electric system controls Synchronization of the propellers and such synchronizing system provides for the selection of one engine of the aircraft to operate as a master engine at a predetermined r.p.m. as selected by the pilot, with the r.p.m. of the other engines being controlled according to the master engine r.p.m. Accordingly, an electric generator is provided for each engine for producing a control voltage having a frequency determined by the r.p.m. of the engine, and synchronizing and control equipment is provided for comparing and for utilizing the signals from the generator of the master engine and the other generators in Such a manner that the other engines function as slaves in relation to the master engine. The synchronizing system is so designed for a four engine aircraft as the DC-6 Such that either one of two engines may be Selected as a master engine for the other engines to follow.

A mechanical limiting device is incorporated into the synchronizing system for limiting the amount of control which the master engine has over the slaves, Such that in the event the master engine fails, the slave engines will nevertheless remain effective. By reason of such limiting device the slave engines will follow changes in the master engine r.p.m. for only about t3% of their speed. If the slave engines are outof synchronization by more than about 3% they can normally be brought within the master engines range by working toggle switches of the stray slaves. However, to make it easier, means including a resynchronizing button are provided whereby each push of Such button provides for a 3% return of all stray slaves. The resynchronizing button is pushed aS many times as may be necessary to bring the slaves into synchronization with the master engine.

The propeller controls usually installed on the flight engineers main instrument panel includes the master control lever by means of which the r.p.m. of all engines can be changed simultaneously, toggle switches corresponding in number to the number of engines for con-- trolling the r.p.m. of the engines individually, a Synf. ICC

cronizing switch for turning the synchronizing system on .or off and for selecting the master engine in a four engine lsimulated by novel coordinated electrical computing means and control apparatus so that aircraft personnel can obtain on the ground by the use of this invention complete and thorough training in the operation of such systems.-`

The invention will be more fully Set forth in the following description referring to the accompanying drawings, and the features of novelty will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In the drawings and Specification the invention is shown and described as applied to a four engine aircraft of the DO-6 type in which either one of two engines, called master-follower engines, may be selected as the master engine whereupon all other engines including the other master-follower engine become slaves; VFor the purpose of simplifying the drawing and specification Simulated propeller r.p.m. control and synchronizing apparatus is shown and described only for three engines, the number 2, 3 and 4 engines of the aircraft, engines 2 and 3 being master-follower engines each of which can be utilized as either a master or follower engine, and the other engine, the number 4 engine,

-the Simulated propeller r.p.m. control and synchronizing apparatus including a toggle servo (AN) with control circuitry for each engine system;

Fig. 3 is a similar illustration of another portion of the simulated propeller r.p.m. control and synchronizing apparatus comprising a band limit Servo (AS) and control circuitry for each slave engine system (not including the No. l engine); and

Figs. 4 and 5 are illustrations of portions of the Simulated propeller r.p.m. control and synchronizing apparatus including control relay energization circuitry common respectively to all engine systems and to the two slave engine systems (not including the No. l engine) only.

As will be seen hereinafter the Speeder rack or governor Servos function according to various control factors to simulate the operation of governor means in the aircraft determining the r.p.m. of the engine. Each toggle servo is eifective upon toggling, i.e.,individual speed control of its particular engine, to maintain its Speeder rack Servo in position corresponding to the new desired speed and prevent the return of such Speeder rack servo to its initial position before toggling. The band limit servos which are associated with only Such engines as are or operate as slave engines (follower engines), are effective to limit the band or range ofv syncronization of respective associated Speeder rack servos with the master Speeder rack servo to about i3% as previously stated.

In the drawings a number of simplifying conventions have been adopted vto facilitate tracing of the circuitry and to avoid unnecessary and Vconfusing repetition of description of Such structure as yis the Same in each of the systems corresponding to the No. 2, No. 3, and No. 4 engines. Referring to Fig. l for example, it is noted that the parts of the engine No. 3 system are identified by a four digit reference numeral, whose thousands digit is three, and the corresponding parts in the engine No. 2 and engine No. 4 systems are identified by corresponding reference numerals whose thousands digits are two and four respectively. In considering the systems, reference is explicitly made to the parts of the engine No. 3 system,

but the corresponding parts of the engine No. 2 and' engine No. 4 systems should be considered simultaneously. As stated previously, the No. 2 and No. 3 engines are master-follower engines whereas the No. 4 engine (and also the No. l engine not described herein) are slave engines. The No. 3 engine `may be assumed for the time begins to be the master engine, so that the No. 2 engine behaves as a slave engine much like the No. 4 engine. The structure of the No. 3 engine system will be described at great length, but the structure of the No. 2 and No. 4 engines will be described only to the extent necessary to point out distinctions from the structure of the No. 3

engine. The interdependence of operation of all engine systems will be described in great detail. Other parts of the drawings, common to two or possibly all three of the described engine systems, will be identified by reference numerals having less than four digits or by appropriate letters, as will appear hereinafter.

In Fig. l of the drawings, reference character 3002,

Vdesignates the Speeder rack servo (SR3) for the No.

3 master engine. Speeder rack servo 3002 is typical of other servo systems shown in the drawings. Referring to the Speeder rack servo 3002 as an example, such servo includes a servo amplifier 3004 to which are applied a number of control voltages, a motor 3006 responsive to the amplier output, and a number of potentiometers including an answer c ard 3008 and other potentiometer cards as for example 3010 and 3012 having slider contacts connected through a gear reduction box 3014 to the motor. Servo amplifier 3004 is a summing amplifier for determining the resultant of the input voltages, and is of a type well-known in the art for algebraically summing a plurality of A.C. voltages of varying magnitude and polarity. A detailed circuit illustration of the servo amplifier is therefore unnecessary.

For purposes of simplicity the motors of various servos in the system have in places been diagrammatically illustrated by means of a rectangle inclosing the letter M.

Motor 3006 is of the two-phased type, the control phase 3016 of which is energized by the amplifier output as illustrated, the other phase 3018 being energized by a constant reference A.C. vol-tage el de-phased 90 from the control voltage. The operation of this type of motor is well-known, rotation being in one direction when the phase dierence between control and reference voltages of the respective phases is +90, and` in the opposite direction when such phase difference is -90. The rate of rotation in both cases depends on the magnitude of the control voltage.

It should be understood that the motors used -herein generally are at a standstill. They rotate yresponsive to a change in a control signal applied from some point external to the associated servo amplifier and even then rotate only for a short time interval until the change in the external input signal has been rebalanced. Rebalance is due to a change in magnitude and/or reversal of phase of a negative feedback type or answer signal, designated as ANS or CAL which said change in magnitude and/ or reversal in phase tends to oppose the effect of further rotation due to the change in the external input signal. The answer signal is generated continuously in accordance with the instantaneous position of the servo motor and as such is applied also to the linput of kthe associated servo amplifier'. Because the answer signal "is generated within the servo system in question ,it will also be referred to as an internal input signal as distinguished from the aforesaid external input signal.

Except for the aforesaid A.C. voltage e1, al1 A.C. voltages used herein are either in phase with or in phase opposition to another A.C. `reference voltage +B. Still another A.C. reference voltage -E is also provided and is of equal magnitude but in phase opposition to the reference voltage +E. Only one D.C. voltage is used in the system and this is identified as +B (D.C.). It is employed chiey for energization of relays. Therefore al1 voltages other than this voltage +E (D.C.) may be assumed to be A.C. voltages of the same line frequency, even though not so explicitly identified or labeled, and their n-phase kor phase :opposition to the reference voltage +B is indicated by a `plus sign or a minus sign respectively.

The motor 3006 serves to operate through gear reduction box 3014 and suitable mechanical connections indicated by dotted .line 3020 contacts 3022, 3024 'and 3026 of potentiometers 3008, 3010 and 3012 respectively. The potentiometer resistance elements such as 3008 of the speeder rack servo (SRS) and `other potentiometers indicated in the drawing may be of the well-known wound card type and are of circular band form in practice, but are diagrammatically illustrated in plane development for clarity. A structural arrangement that may be conveniently used for a servo motor and potentiometer combination of the character above referred to is shown in Patent No. 2,431,749, issued December 2, 1947, to R. B. Grant for Potentiometer Housing `and Positioning Structure.

It will be apparent that operation of the servo motor in either direction causes the gang operated potentiometer slider contacts, such as slider contact 3022 to move to corresponding angular positions on the respective potentiometer elements for deriving, i.e. picking oi potentiometer voltages depending on the respective contact position. Each potentiometer of each servo system is shaped or con-toured and designed with suitable shunting resistances as required so that the Value of the derived voltage at the potentiometer Contact bears a certain rela.- tionship to linear movement of the slider contact depending upon the particular lfunction of the potentiometer, and has an A.C. voltage impressed across its terminals depending as to instantaneous polarity and magnitude also upon the function of the potentiometer.

The speeder rack 'servo (SR3) has slider contact 3026 of its potentiometer 3012 connected over the ,normally closed (NC) contact L of engine seize Yrelay 3028 with an input of an r.p.m. servo v3.03.0 associated with the engine No. 3 system whereby operation Vof the rpm. servo may be controlled by the SRS servo. Potentiometer card 3012 has one end grounded and the other end supplied by the reference voltage +B. As shown the r.p.m. servo controls an r.p.m. indicator 3032 which registers simulated engine rpm. -of engine No. 3. The SRS servo functions between limits representing the limits of governor regulation, namely 1.200 :r.p.m. and 2800 rpm., and the r.p.m. registered Von the .r.p;m. indicator 3032 is dependent at any .particular time .upon the SR3 serve position except on 4infrequent occasions Ias for example when the apparatus is operated k'to simulate the condition of insufficient powerbeing vavailable to maintain an engine r.p.m. corresponding to a maximum governor setting, `or a condition `of Vengine seizure. vMeans are provided for supplying the rpm. servo with an input over line 3034 when required for taking into account the described condition 'of ,insu'iiicient power being available, but such means do not `constitute a part of my invention and Aare vtherefore not shown. The relay 3028 whichrrnayv'be controlled "by .an4 instructor in any .inputs to .the r.p.rn;.;servo by `opening the NCfcontat l in line 3034 when the relay picks up thereby causing the. r.p.m. servo to run to a zero reading.

Potentiometer 3010 of the SRS servo has conducting portions only at opposite ends 3036 and 3038 which connect with an indicating lamp 3040 and thence to ground. A circuit is complete for the lamp 3040 only when the slider contact is positioned at one or other of the ends of card 3010 corresponding to one of the limiting positions for the SR3 servo representing a governor setting of 1200 r.p.m. or 2800 r.p.m. respectively. At such time the supply Voltage +B (D.C.) is connected to the circuit for the lamp 3040 which lights to indicate a maximum or minimum governor setting. It is apparent that card 3010 even though outwardly appearing as a potentiometer, actually operates as a switch to open and close a lighting circuit for lamp 3040.

-Inasmuch as many of the inputs to the SRS servo as well as to the other servos are applied through relay contacts, the energization circuits for these relays and the conditions precedent for their energization will be -discussed next. The energization paths for theserelays (hereinafter referred to collectively as internal control relays as distinguished from the engine seize relays) are illustrated in Figs. 4 and 5. Referring to Fig. 4 there .are shown, in simulation of the controls in an actual aircraft, a master r.p.m. control lever 12, a synchronization switch 14, and toggle levers 3042, 2042 and 4042, the toggle levers being associated respectively with the No. 3, No. 2 and No. 4 engine systems. The synchronization switch 14 is a 3-position switch and has two oil-positions corresponding to the selection of the No. 2 or the No. 3 engine as the master engine, and a centerolf-position. When switch 12 is placed in its center oilposition, synchronization of the slave engines with the master engine is precluded. if synchronism were to be maintained even though the synchronization switch 12 is in its center oil-position, the individual toggle levers 3042, 2042 and 4042 would have to be operated.

The master r.p.m. control lever 12 is continuously operable between two limits corresponding to engine governor settings of 1200 r.p.m. and 2800 r.p.m. The upper limit 2800 r.p.m. is also referred to as the calibrate position for reasons that will be apparent hereinafter. The toggle levers are 3-position switches and are usually positioned in a center off-position. The effect of switching a toggle lever to the left-hand position (as viewed in the drawings) is to increase the r.p.m. of the associated engine and conversely the etfect of switching the toggle lever to the right-hand position is to decrease such r.p.m.

The energization paths for the internal control relays shown in Fig. 4 extend from the -l-E (D C.) line 15 to a ground line 16. The energizing circuit for a master engine relay 17 extends from the -l-E (D.C.) line 15; through the relay coil; over line 18 to a contact 19 gang-operated with the synchronization switch 14; then, assuming that the No. 2 engine has been selected as master engine, through contact 19 over lines 20 and 21 and through a usually closed synchronization fail contact 22 to ground. Contact 22 is usually closed but may be opened by the instructor to simulate synchronization failure in which case its elect is the same as though the Synchronization switch 14 were placed in its center oft-position. For convenience in terminology the contact 19 in its No. 2 position, lines 20, 21 and the synchronization fail contact 22 in its usually closed position will be collectively referred to as the master engine relay ground return. i

Automatic relay coil 23 has one end connected to the -l-E (DC.) line 15 and its other end is connected over lines 24 and 25, a contact 27 gang-operated with the synchronization switch 14 provided such contact 27 is in either the engine No. 2 or engine No. 3 position, line 21, and .usually closed synchronization fail contact -22 to ground. For convenience in terminology line 25,

. 6 the switch 27 in either the engine No. 2 or No. 3 position, li-ne 21 and the contact 22 in its usual position will be collectively referred to as the usual ground return. This is the ground return under usual synchronized operating conditions, which presuppose that the engines are in synchronism and operate at some speed less than 2800 r.p.m. but no less than 1200.r.p.m., and lthat the entire system including control lever 12 has been calibrated In such case the lever 12 operates indeed as a calibrated indicating device whose position reiects the r.p.m. of each engine. It is also possible to synchronize the engines by operation of toggle levers, but in such case the position of lever 12 no longer retlects engine r.p.m. and calibration in that sense is lost.

The three master lever relays 3044, 2044 and 4044 may be considered together in much the same manner as the three speeder rack servos have been considered together. Only the relay 3044 of the No. 3 engine system is expressly described, the other being implicitly described by correspondence of reference numerals. The energization path for the No. 3 master lever relay 3044 extends from the -{E (DC.) line 15; then, assuming the toggle lever 3042 is in its center oit-position, through a contact 3046 gang-operated therewith, through the relay coil and over line 3048 to the usual groundy return. As will be apparent hereinafter under usual synchronized operating conditions the three toggle levers 3042, 2042 and 4042 are in fact in the center off-position. The remaining internal control relay which is energized over the usual ground return, is a synchronizing relay 30 is usually in the position as shown in the drawing toconnect to line 26, over such line 26', through the relay coil and through either the normally closed (NC) or the normally open (NO) contact l of the master engine relay 17 depending on selection o f the No. 3 or No. 2 engines as master engine respectively. Nonnalcy as used herein with reference to relay contacts follows the customary convention of the state of such contacts were all sources of relay energization disconnected. The alternative paths from either the NC contact 1 or NO contact of the master engine relay 17 are closely analogousand can be traced simultaneously, even though only the former is explicitly described, by recognizing the correspondence of reference numerals. The path from the NC contact l extends over a line 3050 to a cam operated contact 3052, then over the line 3054 to the -l-E (D.C.) line 15. The contact 3052 is operated by means of a cam 3056, which in turn is gang-operated by the No. 3 RPM servo 3030 previously described. The contact 3052 is usually connected to line 3054 corresponding to an r.p.m. of the No. 3 engine,-as computed by servo 3030, of greater than 400 r.p.m. For an engine speed of 400 r.p.m. or less which corresponds to engine stalling, the cam 3056 operates to open the connection of 3052 thereby opening the energization circuit of the synchronizing relay 30.

In the event the master r.p.m. control lever 12 is positioned to the calibrate position of 2800 r.p.m. the connection of relay 30 to the usual ground return is opened by disconnection of the cam-operated contact 26 from line 26 and as a consequence the synchronizing relay 30 is necessarily deenergized. The contact 26 is connected to line 32 instead. For convenience in terminology the path including line 32, contact 26 in its unusual position, line 25, contact 27 provided it is either in 4the No. 2 or No. 3 position, line 21 and contact 22 to ground will be collectively referred to as the calibrate ground return, corresponding to the master r.p.rn. control 12 in the 2800 rpm. calibrate position. This calibrate ground return is so named because it is complete during calibration, i.e. with lever 12 in the 2800 r.p.m. calibrate position. This, as previously stated, calibrates the systern in that thereafter the position of lever 12 indicates the r.p.m. of each engine.

Before considering the internal control relays which are or may be energized due to completion of the calibrate ground return, it is pointed out that the automatic relay, the three master lever relays 3044, 2G44 and 4044 and the synchronizing relay 30 are usually energized. The automatic relay is usually energized because the usual ground return path is usually complete. The three master lever relays are usually energized for the sarne reason and for the further reason that their respective toggle levers are in the center oit-position under usual synchronized operating condition. The synchronizing relay 3% is usually energized because the usual ground return is usually complete, the lever 12 is usually in a position corresponding to less than 2800 r.p.m., and the r.p.rn. servos of the No. 2 and No. 3 systems are operating at greater than 400 r.p.m. With the No. 3 engine selected as the master engine by virtue of positioning of the synchronizing switch 12 in the No. 3 position, the master engine relay ground return is `open and therefore the master engine relay i7 is necessarily deenergized. Arbitrarily the deenergized state of master engine relay 17 corresponding to selection of the #3 engine as master engine is also deemed as usual, even though under usual synchronized operating conditions the #2 engine could as well be selected as master engine whence relay i7 would be energized.

The relays whose energization paths extend through the calibrate ground return include one calibrate relay and one calibrate lock relay for each engine system. Again the energization paths for the calibrate relay 3%53 and for the calibrate lock relay 3%@ of the engine No. 3 system will be explicitly described whereas the correspending relays of the No. 2 and No. 4 systems will be recognized by correspondence of reference numerals. The energizing circuit for the calibrate relay 13u53 extends frorn the -l-E (DC.) line l through the relay coil and then over the NC contact l of the calibrate lock relay 3050 to the calibrate grdund return. The

immediate consequence of closing the calibrate ground return circuit due to positioning of the master r.p.rn. lever 1?- in the 280() r.p.rn. calibrate position is the energization of the calibrate relay3058. As will be more fully explained hereinafter, after a short time delay the calibrate lock relay 3066 picks up and its NC Contact l necessarily is opened, deenergizing the calibrate relay 3G58. Thus the calibrate relays are energized only with the master r.p.rn. control l2 in the 2800 r.p.m. calibrate position and even then only energized momentarily. With placement of the master r.p.rn. control lever 12 in the 2800 r.p.rn. calibrate position, the SRI., servo 3h62 will run to a position corresponding to 2800 rpm. whereas the toggle servo of the engine No. 3 system (AN3) generally indicated as 3662 will assume a center position defined as undetlected zero, unless it is already initially at such undeiiected center position. As will be more fully explained hereinafter the undeilected zero position is the -usual position of the toggle servos, prevailing under usual synchronized operating conditions.

A cam 35354 is operated by the SRS servo to operate a contact 3056 usually so as to cause its disconnection from line i5, but to cause connection therewith when the SRS` servo is in its 280() r.p.m. calibrate position. A cam 3h68 is operated by the ANS servo 3962 to operate a contact -307) usually so as to cause its connection to a line 3072 connected to contact 3%66 in the unde-ilected Vzero position of the AN3 servo, but to cau-se disconnection therefrom otherwise., With closure. of contact 3674i,

either attendant to the ANB assuming its undeflected zero position due to positioning of the master r.p.m. control 12 in the 2800 r.p.m. calibrate position, or because the AN3 servo was in its undeilected zero position even prior to positioning of the control 12, and with the closure of contact 3066 due to the SR3 servo having run to its 2800 rpm. position, the energization path for the calibrate lock relay 3060 is completed. The path extends from the -l-E (DC.) line 15, contact 3065, line 3972, contact 3070 and the relay coil to the calibrate ground return. Its NC contact 1 opens to open the energization circuit for the calibraterelay 3658 which thereafter remains deenergized. A hold circuit for the calibrate lock relay 3060 is established from the +B (D.C.) line l5 over line 3074, its NO contact 2, and through the relay coil to the calibrate ground retln. Thereafter the calibrate lock relay remains energized until the calibrate ground return is opened once more as for example by shifting the master r.p.m control from the 2800 r.p.m. calibrate position.

The energization paths for the remaining internal control relays are shown in Fig. 5 and have ground returns unconnected to the three previously described ground returns. The relays and associated circuitry shown in Fig. 5 are associated with the slave engines only, i.e. the No. 4 engine system `and either the No. 2 or the No. 3 engine, whichever is selected as slave engine. As previously stated it is assumed for the time being that the No. 3 engine is the master engine and the No. 2 engine is a slave engine as indicated by the position of the synchronizing switch d4 in Fig. 4. ln Fig. 5 as well as in the other gures, a part associated With either engine 2 or engine 3, whichever is selected as slave engine, is identified by a four digit reference numeral whose thousands digit is two and whose hundreds digit is three whereas the corresponding part in the engine No. 4 system is designated by a four digit reference numeral whose thousands digit is four and whose hundreds digit is three, the remaining digits being in correspondence. The circuitry of the No. 2 or 3 system and the No. 4 system is to be considered simultaneously although expressly described only for the No. 2 or 3 system. The No. 4 system is recognized by the correspondence of the reference numerals.

Each of the slave systems is provided with a follow-up relay and a resynchronizing relay which operate to some extent as a bistable pair in that the follow-up relay is usually energized and the resynchronizing relay is usually deenergized. Considering the No. 2 or 3 system in Fig. 5 expressly and the corresponding No. 4 system by correspondence of reference numerals, the follow-up relay for the No. 2 or 3 system is designated by reference numeral 23u32 and its resync'nronizing relay is designated by reference numeral 2364. In simulation of the actual aircraft there is provided a resynchronizing button 34 which is shown in its usual undepressed position, and is provided with four contacts operated with the resynchronizing button 34 in unison to lalternately usually closed and usually open positions. The energizing circuit for the follow-up relay 2302 extends from the +B (DC.) line i5, through the relay coil, through the usually closed contact 2 of the resynchronizing button 34, over line 23556 to the center portion of a potentiometer card 2303 which is operated according `to the position of the A82 or 3 band limit servo 2310. The central portion 2312 of card 2398 is insulated from the remaining portions of said card, which remaining portions are connected in the energization circuit of the resynchronizing relay 2364 as explained hereinafter, The grounded slider 2314 of card 2363 is usually positioned to contact the central portion 2312 corresponding to the center position of the A52 or 3 servo defined as the undeflected zero position as in the case `of the toggle servos previously discussed. Slider 2314 therefore fusually completes the energization circuit for follow-up relay 2302 to ground. It is apparentv that the card l2308 although appearing as a potentiometer acts in effect as a switch to connect the energization circuit of either follow-up relay 2302 or the resynchronizing relay 2304 to ground.

Upon energization of the follow-up relay 2302 a hold circuit is established therefor through the NC contact 2 of the resynchronizing relay 2304 and through its own grounded NO contact 1 In Fig. 5 the follow-up relay 2302 is represented as e-nergized, whereas the resynchronizing relay 2304 is represented as deenergized. Such representation is intended to indicate the state of energization or deenergization under usual synchronized operating conditions and is also used for the relays shown elsewhere in the drawings to rellect their usual state of energization or deenergization as a further aid in interpreting the drawings.

The resynchronizing relay 2304 is usually deenergized because the slider 2314 is usually positioned in the central portion 2312 of card 2308. It will pick up only if said slider 2314 is positioned off-center corresponding to the AS2 or 3 servo being deected from its zero position, the usually energized synchronizing relay 30 is energized, and the resynchronizing button 34 is depressed either momentarily or continuously. Unless all three conditions are satised at least initially, the resynchronizing relay 2304 will remain deenergized and as a necessary consequence the follow-up relay 2302 will remain energized. Assuming that the three conditions precedent for the energizat-ion of the resynchronizing relay 2304 are satisfied, an energization path therefor is completed from the -l-E (D.C.) line through the relay coil, through the NO contact 1 of the resynchronizing button 34, through the NO conact 1 of the synchronizing relay, and then over line 2316 through the off-center portions of card 2308 and slider 23t4`to ground. Once the resynchronizing relay 2304 picks up, whether due nto momentarily or continuous depressing of the resynchronizing button, a hold circuit is established therefor from the -l-E (D.C.) line 15, through the relay coil, through its NO contact 1, over line 2318 through the NC contact 1 of usuallyenergized synchronizing relay 30, then over-line 2316 through the oil-center portions of card 2308 and slider 2314 to ground. The resynchronizing relay 2304 will become deenergized once more if the synchronizing relay is deenergized or the slider 2314 is repositioned at undeiiected zero. In the latter case of course the follow-up relay 2302 is energized once more provided the resynchronizing button '34 has been released again.

The description of the input circuitry of the Speeder rack servos in Fig. l will now be resumed. Again the SR3 servo circuitry will be described completely and the other Speeder rack servos should be considered simultaneously having due regard to the correspondence of the reference numerals as previously explained. The amplifier 3004 of the SR2, servois supplied through respective summing resistors with -four external input signals -l-ASg, -AN3, -l-RPMma, iTOGGLE and with an internal answer signal -ANS. The main input signal to the SRS servo is the voltage -l-VRPMma which is applied to the -I-RPMma input through the NO contact 2 of usually energized master lever relay 3044. As will be seen `the input signal -l-VRPMM principally controls the position of the SR3 servo between an upper limit of 2800 r.p.m. and a lower limit of 1200 r.p.m. The circuitry for generating the voltage -l-VRPMma is shown in the upper portion of Fig. l. A potentiometer card 36, whose one end is supplied by the voltage E and whose other end is grounded, has its slider 38 operated in accordance with the position of the master r.p.m. control lever 12 by means of the mechanical connections 40. The Voltage at slider 38 is fed through a summing resistor `to an amplitier 42, and as amplilied fed through the primary 44 uf a transformer 46 to the secondary 48 thereof. One

l0 end of the secondary is grounded whereas the voltage -l-VRPMm is derived from its other end. The voltage -l-VRPMma is maximum corresponding to the master r.p.m. control lever 12. 'in the 2800 r.p.m. calibrate position andis zero corresponding -to the lower limit 1200 r.p.m. position of lever 12.

As stated the voltage -l-VRPMma is applied to the -l-RPMm,l input of servo amplifier 3004- through the NO contact 2 of the usually energized master lever relay 3044. T-ne ANS and -AN3 signals are fed through NO contacts of the master lever relay 3044, namely contacts 1 and 3 respectively, so that the state of energization of the m-aster lever relay 3044 is an important factor in determining the inputs to the servo amplifier. With relay 3044 deenergized the inputs -ANS, -l-RPMma, and ANB are grounded through the respective NC contacts. Even with the relay 3044 energized under usual synchronized operating conditions, the input -AN3 is zero and as Will be seen the inputs -l-ASa and iTOGGLE are also zero, so that the input voltage -l-VRPMma to the amplifier input |RPMma is the only effective external input to the servo amplifier.

The input i-TOGGLE is usually grounded through a contact 3076 which is operable in three positions according to the position of the toggle lever 3042, to which it is connected by means of the connections 3078. In the usual center off-position offtoggle lever r3042 contact 3076 is grounded, whereas in the increase and decrease position of the toggle lever 3042 the contact 3076 and therefore the input iTOGGLE is connected to the reference voltages -l-E and E respectively.

The input -AN3 usually connects through the NO contact 5 of usually energized master lever relay 3044 to a slider 3080 of a potentiometer 3082 which is positioned by the AN3 servo. Card 3082 is energized at opposite ends by the reference voltage -l-E and -E and its center tap is grounded. The servo AN3 usually assumes` its center undeiiected zero position wherein the slider 3080 and therefore the input AN3 -to the servo amplifier 3004 is grounded as previously stated. Before considering the remaining external input -i-AS3 the derivation of the -ANS input will be considered because uniformly applicable to each of the three speeder rack servos, whereas the derivations o-f the inputs -l-AS2 to the SR2 servo and -i-AS., to the SR4 servo differ somewhat from the derivation of the input -l-AS3 to the SR2, servo.

The ANS signal as stated, is derived through the NO contact 1 of usually energized relay 3044, line 3084 and slide1T 3022 of potentiometer card 3008, whose ends are connected tothe reference voltage -E and to ground. The ground end of card 3008 corresponds to the lower limit speed of 1200 r.p.m. for governor operation as determined by the master r.p.m. control 12 in the 1200 r.p.m. limiting position. The other end of the card 3003 which is connected to the reference voltage -E corresponds to a position of the slider 3022 of 2800 r.p.m. as determined by. the master r.p.m. control lever 12 in its other 2800 r.p.m. calibrate limiting position.

The input -l-AS3 is usually grounded through the NC contact 2 of usually deenergized master engine relay 17. On the other hand the input -l-AS2 of the SR2 servo is connected through the NC contact 3 of the same usually deenergized master engine relay 17- to a slider 2320 of a potentiometer card `2322 which is energized at opposite ends by the reference voltages +B and E and has a grounded center tap. Potentiometer 2322 is operated according to the position of the A82 or 3 servo. When the No. 2 engine is selected as the master engine by positioning the synchronizing switch 14 in the No. 2 position (Fig. 4), the respective connections of the +AS3 input to the SR3 servo and the -l-AS2 inpu-t to theSR2 servo are in effect inverted. Selection ofthe No. 2 engine results in energization ot the master engine yrelay 17;

'1'1 whence the -l-AS3 input `is connected through the NO contact 2 of the master engine relay `17 to the same slider 2320, Whereas the -I-AS2 input is connected through the NC contact 5 of relay 17 to ground. Thus the band limit servo AS2-or 3 supplies `an effective input to the particular speeder rack servo which is associated with the master-follower engine operating as a slave engine, whereas the cor-responding input to the master engine speeder rack servo is grounded. This -is desired as the A82 or 3 servo under certain conditions discussed hereinafter operates to limit the band of synchronization of the slave engine with the master engine. On the other hand the band of synchronization of the master engine is not so to be limited. For the same reason the corresponding input -t-AS4 to the SR4 servo is directly connected to the corresponding slider 4320 of a corresponding card 4322 operated in accordance with the A84 servo without passing through any relay contacts, as the No. 4 engine is always a slave engine. However under usual operating conditions the slider 2320 and the corresponding slider 4320 are grounded in any event -to the center tap of their respective potentiometer cards, as their respective band limit servos are in their center, undeflected zero positions as will be apparent hereinafter, irrespective of which engine is selected as the master engine. Therefore the input +RPMm of each Speeder rack servo is the only input which receives an external effective input signal under usual synchronized operating conditions, namely the same input signal -l-VRpMm as determined by the master r.p.m. control lever 12. Under usual synchronized operating conditions also the respective servo motors of the three Speeder rack servos are free to move as will he apparent immediately hereinafter, and the sliders 3026, 2026 and 4026 of respective potentiometers 30l2, 2012 and 4012 assume corresponding positions. This results in the same signal being fed to the vrespective r.p.m. servo and therefore in the same reading of the three respective,

indicators 3032, 2032 and 4032. This holds true over the entire effective governor range of from l200 to 2800 r.p.m.; however certain special situations arise at the limits of 1200 r.p.m. and of 2800 r.p.m. At the limit of 1200 r.p.m. the respective indicator lights lamps 3040, 2040 and 4040 will light, as they will also light at the 2800 r.p.m. limit. Additional events occur at the limit of 2800 r.p.m.; some of these events have already been discussed in the connec-tion with the deenergization of the synchronizing relay, the momentary energization of the calibrate relays, and the energization of the calibrate lock relays. The further effects of positioning the master Ar.p.m. control lever l2 in the 2800 r.p.m. position will be discussed hereinafter under the heading calibration.

The control windings of the three Speeder rack servos may under certain conditions be short-circuited to freeze the respective servo motors and therefore the gang-operated respective sliders of associated poteutiorneters in place. However under usual synchronized operating conditions the servo motors are free to move and to assume positions corresponding to the selected synchronization speed as determined by the setting of the master r.p.m. control lever 12, so that the respective indicators register the same selected speed as previously explained.

The possible short circuit paths for the control windings of the three Speeder rack servos are analogous toy a certain extent and will be considered together to such extent by express description of such path for the Winding 3016 of the SR3 servo only, the paths for the corresponding windings of the other Speeder rack servos being recognized by the correspondence of reference numerals. The path from the lower end of winding 3016 extends over a line 3086, through a contact 3083 to a junction point 3090. Contact 3008 is operable in three positions in accordance with the operation of the toggle lever 3042 to which it is connected by means of the mechanical connections 3078. The circuit path from the lower end of winding 3016 to junction poiht 3090 is complete only with toggle lever 3042 in its center-off position, being opened when toggle lever 3042 is in the increase or decrease position. As previously pointed out the center-off position of toggle lever 3042 is the position under usual synchronized operating conditions.

The short circuit path extends from the upper end of winding 3016 over line 3092 to a junction point 3094. The short circuit path between junction points 3090 and 3094 may be completed through the NC contact 4 of usually energized master lever relay 3044. Becaus-e the master lever relay is usually energized, such shout circuit path is usually incomplete. There is an additional short circuit path provided between junction points 3090 and 3094, but the corresponding additional short circuit paths in the No. 2 and No. 4 systems differ somewhat therefrom necessitating separate consideration.

The additional possible short circuit path for winding 3016 continues from junction point 3090 through the NC contact of usually energized follow-up relay 2302 and through the NO contact 4 of usually deenergized master engine relay 17 to jurztion point 3094. It is usually incomplete because neither contact is usually closed. The additional possible short circuit path for winding 2016 continues from junction point 2090 through the NC contact of usually energized follow-up relay 2302 and through the NC contact 5 of usually deenergized master engine relay 17 to j unction point 2094. It is usually incomplete because the former contact is usually not closed. The additional shont circuit path for winding 4016 continues from junction point 4090 through the NC contact 2 of usually energized follow-up relay 4302 to junction 50mi 4094. n is usually incomplete because this contact is usually not closed. Completion of the additional short-circuit paths requires deenergization of the respective follow-up relay, and in the case of the No. 2 and No. 3 systems depends additionally on the choice of which of these two engines shall be the master and the slave engines.

The toggle servos (AN) will be considered next with reference to Fig; 2. Following the previous practice, the ANB servo circuitry will be described expressly whereas the AN2 and AN4 servos should be considered simultaneously with the description of the AN3 servo bearing in mind the correspondence of reference numerals, so long as the three servos are analogous. The AN3 servo is provided with a servo amplifier 3096, a control winding 3098 for the associated servo motor represented together with an associated gear reducer by the letter M enclosed in a rectangle for simplicity, and an answer potentiometer card 3100 and other potentiometers shown in the other drawings, some of which other potentiometers have already been discussed. Card 3100 is energized at opposite ends by the reference voltages E and +E and has a grounded center tap. Its slider 3102. is connected to the servo motor by means'of the mechanical connections 3l04. As will be seen hereinafter the slider 3102 usually connects to the grounded center tap of card 3100 corresponding to the usual undefleeted zero position of the servo. A line 3106 is connected to the slider 3102 at one end and its other end is connected to three branch lines 3106a, 3106i) and 31060. For convenience in terminology the path through card 3100 over line 3105 and slider 3102 will be collectively referred to as the answer return.

The servo amplifier 3096 is provided with two internal inputs -CAL and -ANS, at most one of which may he yconnected to the answer return at any one time whereas the other is then grounded. Upon other occasions both internal inputs are grounded. The external inputs to the servo ampliers are the inputs -i-RPMm, SRE and iTOGGLE. Under usual synchronized operating conditions the' CAL and :tTOGGLE inputs to the servo arnpli-er lof each toggle servo (AN) are grounded, and

gestage therefore single description for all three servos will sutlce. The CAL input is grounded through the NC Contact 1 of usually deenergized calibrate relay 3058. During the aforedescribed momentary period of energization of the calibrate relay the CAL input is connected through the NO contact l of the relay and over branch line 3106i: to the answer Teruel. The TOGGLE input isl usually grounded through a Contact 3108 which is operated in three positions according to the position of the toggle lever 3042, to which it is interconnected by means of the connections 3078, provided the toggle lever 3042 is in its center off-position. When the toggle lever 3042 is placed in its increase position, the TOGGLE input connects through contact 3108 to the reference voltage -E, whereas when the toggle lever is placed in its decrease position the input connects through contact 3108 to the reference voltage +B.

The inputs ANS, and -l-RPMm., and SR3 are not completely analogous as regards the circuit paths for their respective input signals in the three servo systems. Moreover under usual synchronized operating conditions the respective inputs thereto are not the same for the three servos, all three inputs being usually grounded for the master engine whereas the slave engines receive eiective signals at their respective inputs -l-RPMma and SR and also at their respective input ANS, However the input ANS for each slave engine toggle servo is also grounded by reason of the grounding of the answer return through the center tap of the associated answer card in the usual undeflected zero position of the respective servo. The input circuit paths for the ANS, -l-RPMm and SR inputs will be considered together and also by a single description for the three servos to the extent applicable. Referring to the AN3 servo expressly, its three input signals ANS, -I-RPMma and SR3 feed through the NO contacts l, g and 3 respectively of the usually energized automatic relay 23. In the event that the automatic relay releases, by reason of placement of the synchronization switch 14 in its center oit-position for example (Fig. 4), each of the three signals is grounded through the respective NC contacts of the automatic relay. Assuming that the automatic relay 23 is energized as it usually is, the three signals are fed to its three NO contacts from the three NO contacts 5, 6 and '7 of usually energized master lever relay 304`4 espectit-fely. Assuming that the master lever relay is deenergized whereas the automatic relay is energized, which conditions concur with the synchronization switch 14 in either the No. 2 or No. 3 position and the toggle lever 3042 being positioned in its increase or decrease position, the path for the ANS signal extends instead through the NC contact of master lever relay 3044 and branch line 3106!: to the answer return; the path for the -lRPMma input signal extends instead through the NC contact of master lever relay 3044 to the voltage -i-VRPMma; and the path of the SR3 input extends instead through the NC contact '7 of master lever relay 3044 over line 3110 tto the slider 3112 of a potentiometer card 3114 which is grounded at one end and supplied by the reference voltage E at its other end. Another line 31111 also connects to slider 3112.

As shown the slider 31-12 is operated according to the position of the SR3 servo. For convenience in terminology the return through card 3114 and slider 3112 will be referred to as the speeder rack return. Connection of the ANS, -l-RPMma and SR3 inputs respectively to the answer return, the voltage -l-VRPMma and to the Speeder rack return requires energization of the automatic relay 23 and deenergization of the master lever relay 3044 as stated, and such deenergization of the master lever relay requires positioning of the toggle lever 3042 in either its increase or decrease position. The shift of the toggle lever from its center oit-position necessarily results in application of the refer- 14 Y ence voltage E or -l-E to the TOGGL input alsoas previously stated and also necessarily results in opening the short circuit for winding 3098 due to the shift from the `center position of another contact 3116 also operated by the toggle lever 3042 and connected thereto by means of the connections 3078. As a result the AN3 servo will be free to move to a position as determined by the now effective external signals to the inputs -l-RPMma, SRS and iTOGGLE and the slider 3102 will be posi-- tioned accordingly. As a .result the input, ANS will receive from the answer return a non-zero signal in ac cordance with the position of the slider 3102.

Reverting to the usual condition of energization of4 both'the automatic relay 23 and the master lever relays the further paths from the contacts of the automatic re lay 23 for the signals to the three inputs ANS,. -l-RPMma and SR differ for the three servos and will? be discussed individually. The further paths for the AN3, servo extend through the NO contacts and Z of the master lever relay 3044 respectively and then to ground over the NC contacts 6, 7 and 8 of usually deenergized' master engine relay 1"7 respectively. On the other hand? the corresponding paths for the AN2 servo, which is as-I sociated with the No. 2 engine which in turn is assumed'. to operate as a slave engine in view of the very deenergization of the master engine relay A17, and of the AN4 servo,I which is associated with the No. 4 slave engine, extend to their respective answer returns, the voltage -l-VRPMma, and Speeder rack returns. In the event the No. 2 engine is selected as the master engine by positioning the synchronization switch 14 to the No. 2 position 4(Fig. 4) with the attendant energization of the master engine relay 17, the relations ot the ANS, -l-RPMma and R inputs of the AN3 and AN2 servos are inverted. The A inputs of the AN3 servo will be returned respectively to the answer return, the voltage |VRpMma and the speeder rack return, whereas the corresponding inputs of `the ANZ servo will all be grounded, and whereas the corresponding inputs of the AN., servo will remain connected to its answer return, the voltage -I-RPMma and its speeder rack return respectively. The aforegoing presupposes that the synchronizing relay 30 is also energized as it usually is, for the non-grounded paths for the ANS, -I-RPMnua and SR inputs of each servo feed through NO contacts of the synchronizing relay 30 as well. As

a general proposition the synchronizing relay 30 will of j course be energized when the automatic relay 23 and the master lever relays are also energized. The condi-` tions whereunder the master lever relays and the automatic relay 23 are energized whereas the synchronizing relay 30 is deenergized arise `due to opening of the ener-- gizationlcircuit for the synchronizing relay 30 by virtue of calibration or of external engine seizure of the RPM No. 3 engine or RPM No. 2 engine (see Fig. 14).

Assuming that the automatic relay 23, the master lever relays and the synchronizing relay 30 are, as is usual, all energized, the complete path to the answer return for the input signal to Vthe ANS input of the AN4 servo is over the NC contact '7 of the automatic relay 23, the NO contact 5 of the naster lever relay 4044, the NO contact Q of-the synchronizing relay 30 and `branch line 410611; the complete path for its -l-VRpMma signal to the -l-RPMma input is over, the NO contact 8 of the automatic: relay 23, the NO contact 6 of the iii-aster lever relay 4044 and the NO contact l' of the synchronizing relay 30; and the complete path-t-o its Speeder rack return for its SR4 input is over the NO contact 9 of the auto matic relay 23, the NO contact '7 of the master lever' relay 4044, the NO contact 11 ofthe synchronizing re lay 30 and line 4111. As gutted the No 2 engine is1 operating as a slave engine so that the master engine relay 17 is deenergized, yin which case the ANS, -l-RPMma, and SR2 inputs are connected to the associated answer return, the voltage -l-VRPMM and the associated Speeder rack return respectively as follows: over the NO contact 4 of the automatic relay 23, the No contact of the master lever relay 2044, the NC Contact Q of master engine relay 17, the NO contact 6 of the synchronizing relay 30 and branch line 2106b; tfer the NO contact 5 of automatic relay 23, Ithe NO contact 6 of the master lever relay 2044, the NC contact 1() of rh-ester engine relay 17 and the NO contact '7 ofth-e synchronizing relay 30; and over the NO Contact 6 of automatic relay 23, the NO contact 7 of master lever relay 2044, the NC contact 11 of m-aster engine relay 17, the NO contact 8 of sylroniz-ing relay 30 and line 2111. The corresponding inputs of the master engine toggle servo AN3 are grounded through the NC contacts 6 Z and of the master engine relay 17 respectively.

y1f the No. 2 engine is selected as the master engine resulting in energizaticn of the master engine relay 17, the three inputs to the ANZ servo in question are grounded through the NO contacts 9, 10 and 11 of the master engine relay 17 respectively, and the c o-rresponding inputs for the ANS servo are lifted ofi ground and are returned to its answer return, the voltage -l-VRPMM and its Speeder rack return over the following complete paths respectively: over the NO contact of automatic relay 23, the NO contact 5 of master l-e-ver relay 3044, the NO contact 5 of master engine relay 17, the NO contact 5 of synchronizing relay 30 and branch line 3106b; the NO contact 2 of automatic relay 23, the NO contact 6 of masterlever relay 3044, the NO contact Z of master engine relay 17 and the NO contact 4 of synchronizing relay 30; and the NO contact 3 of automatic relay '23, the NO contact 7 of master leider relay 3044, the NO contact 8 of master engine relay 17, the NO contact 5 of synchronizing relay 30 and line 3111. Under the special aforedescribed circumstance Where the automatic relay 23 and the three master lever relays are energized whereas the synchronizing relay 30 is deenergized, the three inputs -ANS, -l-RPMma and -SR of each slave engine toggle servo are grounded through their respective NC contacts ci the synchronizing relay 30.

The short circuit paths for the control windings of the toggle servos (AN) will now be described by way of a single description applying to the AN?, servo to the ex tent applicable. Beginning at the lower end of winding 3098 the short circuit path extends over line 3118, through toggle lever contact 3116 provided the toggle lever 3042 is its center off-position, and the NC contact 2 of calibrate relay 3058 provided the calibrate relay is, as usually, deenergized. In the event of shifting of the toggle lever 3042 from its center oit-position to either its increase or the decrease position or during the aforedescribe'd momentary energization period of calibrate relay 3058 the short circuit path is necessarily opened. The short circuit path extends from the upper end of control winding 3098 over line 3120 to the NC contact 3 of usually deenergized resynchronizing relay 2304. fri the event of energization of the resynchronizing relay attendant to the depressing of the resynchronizing button 34 the short circuit pathy is necessarily open. Completion of the short circuit path is different in each servo system necessitating individual consideration.

In the case or" the AN4 servo the short circuitv path is A complete as described as the NC contact of resynchronizing relay 4304 is tiedV to the NCl contact of the calibrate relay 405%, The short circuit path for winding 2003 is complete from the NC contact 2ofits calibrate relay 2058 to the corresponding NC c ontact of the resynchronizing relay 2304 over the interconnecting NC contact E of usually deenergized master enginegrela'y F75 17. If the No. 2 engine is selected as master engine thc short circuit path is alternatively completed through the NO contact 13 of master engine relay 17, energized in such event, :E over a branch line 2121 terminating in line 2120. With the No. 3 engine selected as master engine the short circuit path for Winding 3093 is completed from the NC contact 2 of calibrate relay 3058 over the NC contact l2 of the master engine relay 17 to a corresponding branch line 3121 terminating in line 3120. If the No. 2 engine is selected as the master engine the short circuit path for winding 3098 is complete from the NC contact 2 of calibrate relay 3058 through the NO contact 12 of the master enginerelay 17 and the NC contact lof the resynch-ronizing relay 2304. Completion of the-short circuit paths for the control windings of the toggle servos requires that lthe respective toggle levers be in their center olf-position; that the respective calibrate relays be deenergized with no further requirement in the case of the master engine servo. In the case of a slave engine system, it is additionally required that its resynchronizing relay be deenergized. In View of the usual conditions of the 4relays involved the three windings therefore are usually short-circuited, and as will be seen hereinafter, their servomotors are in the undeected zero positions.

The circuitry of the band limit servos (AS) will be considered next referring to Fig. 3. As previously stated a band limit servo is associated only with a slave engine, whereas the master engine has no band limit servo as its band for synchronization is not to be limited. Referring to Fig. 3, the A82 or 3 servo, which is associated with the engine No. 2 or engine No. 3 system depending on which of these engines is the slave engine, to the extent applicable, will be described expressly whereas the A84 servo is to be considered concurrently having due regard to the correspondence of reference numerals. The A52 or 3 servo is similar to the Speeder rack and toggle servos previously described, in that it is provided with an input ampliier 2330, a control winding 2332, a servo motor represented with the associated gear reducer by the letter M enclosed in a rectangle, and an answer potentiometer card 2334 and other potentiometer cards previously described. Potentiometer 2334 is energized at opposite ends by the voltages -l-E and E and is insulated at its center as indicated by the dotted line 2336 thereby dening an upper and a lower half-potentiometer each of which is grounded 'at its respective center tap. The upper half potentiometer is additionally energized by the voltage -E near the insulation line 2336 and the lower half potentiometer is energized by `the voltage +E also at the insulation line 2336. The upper and lower half potentiometers are each providedwith a slider designated as 2338 and 2340 respectively, which may be positioned according to the position of the servo motor by means of the mechanical connections designated asv 2342 and 2344 respectively. The. sliders, 2338 and 2340 move up and down in unison and therefore pick olf vol-tages of the same magnitude and like sign at any given instant. As previously stated and as will be shown later the usuall position for the servo motor is the undeilected zero position wherein the slider 2338 is connectedy to the upper grounded cententap and the slider 2340- to the lower grounded center tap.

The servo amplifier 2330 is provided with two external inputs -I-RPMmL and ANZ or 3, an internal -ANS input andv another input -MaENG which in some instances may be connected to an external input and in other instances to an internal input, the latter being from the NC Contact 6 of usually energized follow-up relay 2302 i provided the-relay is deenergized, over line 2345.- to' the slider 2338 of the upper half of potentiometer'card'2334'i For convenience in terminology the return over lline 2346 and. slider 2.338V through potentiometer card 2334 willbe' referred to' as the supplemental band limit servo answer return as distinguished from the main band limit servo answer return which permanently connects to the ANS input land as such includes line 2348 and the slider 234i) of the lower half of potentiometer2334, to which slider 2340 line 2348 is connected.

The inputs -l-RPMma, ANZ o, 3 and MaENG can -b'e considered concurrently and to a certain extent as applicable to the AS4 servo having regard to correspondence of the reference numerals. Their circuit paths extend respectively over the NO contact 4 of usually energized follow-up relay 2302 `and the NO- contact 12 of usually energized synchronizing relay 30 tothe voltage -l-VRPMma; over the NO contact 5 of usually energized follow-up relay 2302 to the No Zonnet of usually energized synchronizing relay 30; and over the NO contact 6 of usually energized follow-up relay 2302 to the NO c ontact 14. of usually energized synchronizing relay 30. In the gent that the follow-up relay 2302 is deenergized due to energization of the resynchronizing relay attendant to depressing of the resynchronizing button 34 (Fig. 5), these three inputs will be respectively grounded, grounded, and connected to the supplemental band limit servo answer return through the respective NC contacts of the follow-up relay 2302. In such case the MaENG `and ANS inputs will receive over their respective answer returns signals of the same magnitude and like sign to cause an extremely rapid run-down to the undeilected zero position. The run-down is rapid because of application of two rather than one answer signals.

Assuming that the follow-up relay is energized whereas the synchronizing relay 30 is deenergized as may have been for example in the event that the master RPM control 12 is placed in the 2800 r.p.m. calibrate position (see Fig. 4), the -l-RPMma, AN2 o, 3 and MaENG inputs are each grounded through respective NC contacts of the synchronizing relay 30 in which case the servo motor not controlled by any external effective inputs, answers itself to the undeflected zero position but not as rapidly as under the aforementioned conditions.

In the event that the follow-up relays and the synchronizing relay 30 are energized las usual, the further paths for the MaENG input extends over the NC contact 15 of usually deenergized master engine relay 17 to a sui-der 3130 of a potentiometer card 3132 whose one end is grounded and whose other end is energized by the voltage E. The path for the corresponding input to the A84 servo is analogous and also extends to the same slider 3130 of the same potentiometer 3132 over the NC contact 16 of the master engine relay. The slider 3130 is po-sTioned according to the position o-f the servo motor of the RPM No. 3 servo which in turn iS of course determined according to the position of the SR3 servo. The position of the SR3 servo in turn is usually determined in accordance with the voltage -l-VRPMma. The input -t-RPMm to the servo ampliier 2330, as previously stated, is supplied 'usually directly by the voltage -l-VRPMm. The summing resistor 2350 ofthe -i-RPMma input is properly proportioned with reference to the summing resistor 2352 of the MaENG input that the voltages supplied therethrough to the servo ampliiier 2330 are equal. Inasmuch as these voltages are inherently opposite and inasmuch as the input ANZ or 3 receives usually no effective signal the net external input to the ASZ or 3 servo is usually zero.

If the No. 2 engine is selected as the master engine with the attendant energization of the master engine relay 17, the input circuit to the MaENG input extends over the NO contact l of relay 17 (instead of the NC contact l5) t0 a corresponding slider 2130 of a correspondingpotentiometer 2132 whose one end is also grounded and whose other end is also supplied by the voltage E. .The corresponding input of the AS4 servo continues over the NO contact l of master engine assign 18 relay 17 to the same slider 2130 of the same potentiometer card 2132 which is operated in accordance with the position of the RPM No. 2 servo analogous to the operation of the slider 3130 by the RPM No. 3 servo. In such case the two/inputs -i-RPMma and MaENG will usually remain balanced nevertheless, as the SRZ servo when operating as a master engine servo operates much in the manner as the SR3 servo when it (the SR3) operates as a master engine servo.

The further path for the AN inputs from the NO contacts 13 and E of the usually energized synchronizing relay-30 differ for the ASZ or 3 and the AS., servo necessitating individual consideration. The ANr input extends directly to a slider 4134 of a potentiometer 4136 which is energized at opposite ends by the voltages E and +B. The slider is operated in accordance with the position of the AN4 servo motor and is therefore, in the usual undeected zero position of the AN4 servo, connected to the grounded center tap, so that the input AN4 is in fact usually zero. 'Ihe further path for the ANZ r3 input signal depends on the selection of the slave engine as between the No. 2 and No. 3 engine systems, being connected to a corresponding potentiometer of whichever toggle servo is the slave engine servo. In other words the AN inputs of the band limit servos are determined in accordance with the position of the respective slave toggle servos in contradistinction to the MaENG input which is determined in accordance with the position of the same master r.p.m. servo and therefore the same master Speeder rack servo. If the No. 3 engine is the master engine and therefore the No. 2 engine the slave engine, the further path for the ANZ or 3 input extends from the NO contact 13 of synchronizing relay 30 over the NC contact 14 ofaster engine relay 17 to a corresponding slider 2m of a corresponding potentiometer card 2136, also energized-at opposite ends by the voltages E and -l-E and also having a grounded center path. The slider 2134 is Vpositioned according to the operation of the slave band limit servo ANZ which is usually in its undeected zero position wherein the slider 2134 is grounded at the center tap of potentiometer 2136, resulting in zero input signal to the input ANZ or 3. If the No. 2 engine is selected as the master engine and therefore the No. 3 engine as a slave engine, the further path for the input ANZ r 3 extends from the NO contact 15 of the synchronizing relay 30 through 4the NO contact-4 of now energized master relay 17 to a correspondingslider 3134 of a corresponding potentiometer 3136, also energized at opposite ends by the voltages E and -l-E and also having a grounded center tap. 'Ihe slider 3134 is positioned according to the operation of the now slave engine toggle servo AN3 which is usually in its. undeflected zero position, so that the slider 3134 is also usually connected to the grounded center tap of potentiometer 3136, which also results in a zero input to input ANZ or 3.

The short circuit path for the control windings of the band limit servos will be discussed next and, insofar as applicable, by a single description with reference to the control winding 2332 of the ASZ or3 servo. Beginning at the lower end of winding 2332 the short circuit path extends over a line 2354 to the contact 18 of usually energized synchronizing relay 30 at whit? contact the path is usually open, requiring deenergization of the synchronizing relay 30 for completion, as for example when the master r.p.m. control 12 is positioned in the 2800 r.p.m. calibrate position (see Fig. 4). Completion of the short circuit path for the two band limit servos under consideration is non-analogous necessitating separate consideration. Considering the AS4 servo tirst, be-

ginning at the upper end of its winding 4332, the 'short circuit path extends over line 4356 over the NC contact of calibrate relay 4058 and then directly to the NC contact 2 2 of the synchronizing relay 'Where it may be completed upon deenergization of the synchronizing relay 30. The circumstances under which the calibrate relay 4058 is deenergized while the synchronizing relay 30 is also deenergized will be discussed under the heading Calibration hereinafter. The short circuit path for the control winding 2332 of the ASZ or 3 servo, beginning at the upper end of the control winding extends over a corresponding line 2356 to the corresponding NC contacts of each of the calibrate relays 3058 and 2058 of theengine No. 3 and No. 2 systems respectively. Completion of the path lto the NC contact 1S of the synchronizing relay 30 depends on which ouf-'the two engines is selected as the slave engine. In the event that the No. 2 engine is the slave engine, the path is completed through the NC Contact 17 of deenergized master engine relay 17, whereas in the-event the No. 3 engine is selected as the slave engine, the path is completed through the NO contact 1'7 of the master engine relay 17, now assumed to be energized. The circumstances under which the synchronizing relay 30 may be deenergized and the calibrate relays 3058 and 2058 also deenergized will likewise be discussed under the heading Calibration.

With the description of the circuitry of the various servos completed, it is Well-Worth at this point to review the usual states of energization of deenergization of the internal control relays and the usual synchronized operating conditions of the various servos as they form the starting point for other modes of operation. Unless otherwise specified hereinafter these relays and servos will be assumed to be in the usual synchronized operating condition. The following relays are usually energized: the automatic relay 23, the three master lever relays 3044, 2044, and 4044, and the synchronizing relay 30. The master engine relay 17 is arbitrarily assumed to be usually deenergized in view of selection of the No. 3 engine as the master engine by positioning the synchronizing switch 14 in the No. 3 position.

The following relays are usually deenergized: the three calibrate relays 3058, 2058 and 4058, andL the three calibrate 'lock relays 3060, 2060 and 4060. Additionally the two follow-up relays 2302 and 4302 are usually energized whereas the two resynchronizing relays 2304 and 4304 are usually deenergized. The three toggle levers 3042, 2042 and 4042 are usually assumed to be in their center off-positions.

The three speeder rack servos (SR) are usually free to move between the limits of 1200 r.p.m. and just short of 2800 r.p.m. and move to like extents responsive to positioning of the master r.p.m. control 12. The only effective input signal to each is the voltage -1-VRPMma, applied to the -l-RPMml, input of each and having a. magnitude in accordance with the position of the master r.p.m. control lever 12. The three toggle servos (AN) usually have their windings short-circuited so that their motors are frozen. The effective inputs of the master engine toggle servo are all grounded, whereas the input --l-RPMma of each of the slave engine toggle servos is returned to the voltage +VRPMm whose value is in accordance with the position of the master r.p.m. control l2. The Speeder rack inputs (-SR) of the slave toggle servos are determined in accordance with the position of their respective Speeder rack servos, whereasv their TOGGLE inputs are usually grounded. Although the slave toggle servos are subject to effective external input signals, namely l-RPMm and -SR they are nevertheless usually in the undefiected zero position as their servo motors are frozen in place dueto the short-circuiting of their control windings. The two band limit servos are usually free to move but neverthelessV are usually in the undeliected zero position as their two respective only external eective Iinputs. -l-RPMm and MaENG are effectively balanced, the remaining effective input -AN from their respective slave toggle servos being usually zero corresponding to their usual uncleiiected zero positions.

The toggle servos and the band limit servos are generally placed in their usual undeected zero positions as the result of initial calibration on take-olf of the simulated Eight, when as in fthe actual plane the master r.p.m. control 12 is placed in the 2800 r.p.m. calibrate position. rfhe calibrate operation will be discussed next.

CALIBRATION For calibration purposes the student pilot positions the master r.p.m. control 12 in the 2800 r.p.m calibrate position (Fig. l). The following description attendant to such positioning is uniformly applicable, with a few stated exceptions, to the servos of each engine system and to such extent specific reference will be made only to the servos of the No. 3 master engine. The servo motor 3006, under the inuence of the maximum -l-VRPMma voltage, runs towards the upper 2800 r.p.m. limiting position causing the slider 3024 to reach the upper portion 3035 of potentiometer card 3010, and the consequent lighting of lamp 3040. Referring to Fig. 4, with lever d2 in the 2800 r.p.m. position the cam 28 is caused to position the contact 26 so as to open connection of relay 30 to the usual ground return and close the calibrate ground return. The synchronizing relay 30 is deenergized and the three calibrate relays 3058, 2058 and 4058 are energized as their energization circuits are completed through the NC contacts 1 of their respective calibrate lock relays 3060, 2060 and-4060. However as will be immediately apparent, the energization of the calibrate relays is only momentary and these relays will be deenergized again upon energization of the calibrate lock relays. Referring again to Fig. l and considering the description of the SR3 servo as applying to the other speeder rack servo as Well, the short circuit path and input circuit paths remain unchanged, but the -AN input, unless it had been zero before, will become zero as the slider 3080 will assume the position connecting to thc grounded center tap of potentiometer 3082. This is so in View of the fact that the ANS servo will run to undeected zero.

The l-AS input of the master engine SR servo had been and remains grounded through a contact of the master engine relay. The AS input of the slave engine SR servos had been and remain connected to respective sliders 2320 and 4320 of the band limit servo potentiometers 2322 and 4322 respectively. These sliders, unless they had been connected to the grounded center-taps of their respective potentiometers before, will now be so connected. This is so because the band limit servos are also running to undeected zero.

Referring to Fig. 2 and again considering the description of the AN3 servo representative, insofar as applicable t0 the other two toggle servos, the short-circuit path for the `control winding 3098 is now opened in view of the energization of the calibrate relay 3058. The ANS servo therefore becomes free to move and it does in fact move to its undellected zero position in view of the fact that the iTOGGLE input remains grounded through toggle contact 3108 in its center off-position as before, whereas the -CAL input is returned through the NO contact of now energized calibrate relay 3058 to the answer reim. The ANs, partum and *sa inputs of the master engine toggle servo had been and remain grounded through contacts of the mas-ter engine relay 17. The corresponding inputs of the slave engine toggle servos are now grounded through respective NC contacts of the deenergized synchronizing relay 30.' The AN servos being subject only to an answer type internal input signal and being free to move, are caused to run to their deiiected zero position wherein the sliders of their answer cards are positioned at the grounded center taps, so that the -CAL inputs are also ultimately grounded;

Referring to Fig. 3 for a study of the eiects of calibration on the band limit servos, the description for the ASZ o, 3 servo is also applicable to the AS4 servo. The inputs -l-RPMma, AN-3 or 3 and -MaENG of the AS3 or 3 servo are grounded, owing to the deenergization of the synchronizing relay 30, respectively through its NC contacts 12, 15 and 14. Its NC contact 1 8 in the short-circu-iiig-Etth for-v vinding 2352 also closes but at the same time the NO contact of the now energized calibrate relay 2058 opens, so that the servo motor of the A82 o, 3 servo remains free to move. If the No. 2 engine had been selected as the master engine resulting in closure of the NO contact 1'7 of the master engine relay the short-circuit path for "wi-riding 2332 would nevertheless remain open due to the opening of the NC contact of the now energized calibrate relay 3058. In view of the fact that the only non-zero input to the AS3 o, 3 servo is lthe ANS input the servo motor will run to the undeflected zero position. When this position is attained the -ANS input will become zero as well.

The aforegoing description of operation of the AS2 or 3 servo speciiically and of the A84 servo by implication presupposed that the follow-up relays were, as usual, energized even during the calibration. Should a yfollowup relay, say relay 2302, be deenergized, as for example upon initial application of power by reason of the fact that the position of the slider 2314 of the AS3 or 3 servo card 2308 is then random, and therefore possibly not at the undeflected zero position (Fig. 5), the servo will nevertheless run to the undeflected zero position during calibration. Referring again to Fig. 3 and again implicitly considering also the A84 servo, in such case the inputs -I-RPMma and -AN3 o, 3 will again be grounded as in the previous example but now through the NC contacts 4 and respectively of the follow-up relay 2302. The- MaENG input will be returned to the supplemental band limit servo answer return through the NC contact 6 of the follow-up relay 2302, now assumed to be deen-ergized, so that the servo amplifier 2330 will be subject only to two answer signals applied to the inputs -MaENG and -ANS. This will cause the aforediscussed rapid rundovm of the servo motor lto the undeected zero position. Referring to Fig. 5 with the grounded slider 2314 connected to the center portion of card 2308 in the undeected zero position `of the servo, the energization path for the lfollow-up relay 2302 is now complete, so that the relay is energized and thereafter holds itself through its grounded NO contact 1. Referring again to Fig. 3, its NO contacts andare closed returning the inputs -l-RPMma, -ANZ or 3 and -MaENG to ground rmpectively through the NC contacts 12, 13 and 1 4: of the deenergized synchronizing rela-y 3i? The follow-up relay 2302 has contacts 2 and 5 respectively in the short-circuiting paths for the c ontrol-windings of the SR3 and SR3 servo, but the state of energization or deenergization of the follow-up relay at this time is immaterial as the short-circuit paths for these windings are opened through the NO contacts l of their respective calibrate relays.

Referring to Fig. 4, as a consequence ofthe attainment of the undeected zero position by the toggle servos and of the 2800 r.p.m. position bythe Speeder rack servos, the three calibrate lock relays will be energized and therefore the three calibrate relays will be deenergized again. The description of the energization of the calibrate lock relay 3060 is intended to be equally applicable to lthe description for the calibrate lock relays `of the other two systems. The energization path of the calibrate lock relay 3060 extends from the |E (D.C.) line 15 through the cam operated contact 3066 now connected thereto in View of the SR3 servo having attained .the 2800 r.p.m. position, line 3072, and contact 3070 now connected to line 3072 in View of the AN3 servo having attained its undeflected sarily lbe either energized or deenergized.

zero position, and through the relay coil to Ithe calibrate ground return. Its NO contact 2 closes establishing a heid circuit from the +B (no.) une is through the No Contact 2 and the relay coil to the calibrate ground return. On the other hand its NC contact 1 opens thereby opening the energizing circuit for the-calibrate relay 3058 which now releases. Referring again to Fig. 2 with the release of the calibrate relay 3058, its NC contact 2 closes again thereby again completing the short circuit path for the con-trol winding 3098. The servo motor is frozen in the undeected zero position and at the same time the input -CAL is now grounded through the NC contact l of calibrate relay 3058 again, instead of through the NO contact 1 and answer return. The circuit conditions of the toggle servos remain otherwise the same. Referring to Fig. 3 again, the short-circuit paths for the control windings of the band limit servos will now be complete for the first time owing to the deenergization of the calibrate relays, coupled with the presently prevailing deenergization of the synchronizing relay 30. These two states of deenergization are necessary and suicient per se for the short-circuiting of the control winding 4332 of the AS., servo, whereas in Ithe case of the short-circuit path of control Winding 2332 of the AS3 o, 3 servo these two conditions are also necessary and suiiicient, as the master engine relay 17 must neces- If it is deenergized the short-circuit path is completed vfrom Ithe NC contact 18 of the synchronizing relay 30 and the NC contact of the calibrate relay '2058 over the NC contact 1'7 of relay 17, whereas if the master engine relay i7 is ergized by selection of engine No. 2 instead of engine No. 3 as the master engine, the short-circuit path is completed from the NC contact 18 of the synchronizing relay 30 through the NO contact 'of the master engine relay 17 to the NC contact 5 ocalibrate relay 3058. The circuit conditions for The band limit servos remain `otherwise the same and the circuit conditions for the Speeder rack `servos of course are not affected by the state yof energization or de-energization of the calibrate relays in any event and therefore remain the same.

W-ith the deenergization of the calibrate relays calibration is complete and the apparatus remains in the state as at :the end of calibration until the student pilot again operates the master r.p.m. control lever l2 to a position corresponding to less than 2800 r.p.m., as a consequence of which the usual synchronized operating conditions will again prevail. Inasmuch as the circuit conditions corresponding to the usual synchronized operating conditions have already been summarized, they will not be repeated here except to recall that the short circuit paths for the control windings of the band limit servos are opened again, enabling the respective servo motors to move once more from the undefleoted zero position. However, during the usual synchronized operating conditions the band limit servos will stay at their respective undeilected zero positions, irrespective of the position of the master r.p.m. control lever l2, because their only eiective external inputs -l-RPMma and -MaENG will remain equal and opposite. With the circuit conditions prevailing under usual synchronized operating conditions known, the changes in such condition owing to toggling, i.e. manual speed control of a particular engine, may be considered. However this subject matter will be treated under two separate headings Sync. Oif-Toggling and Sync On-Toggling corresponding to the toggling operation with the synchronization switch 14 in its center off-position and in either of its No. 2 or No. 3 on-positions, respectively.

SYNC. OFF-TOGGLING The starting pointV for sync. oi-toggling are the usual synchronized operating condition wherein the Speeder.

rack servo motors are positioned corresponding to an engine speed of less than 2800 r.p.m. 'Ihe student pilot positions the synchronizing switch 14 in -its center olfposition with the result that the usual ground return, the master engine ground return and the calibrate ground return are all opened with switch contact 27 in its center oit-position, thereby deenergizing all relays whose energization paths are shown in Fig. 4 unless such relays had been deenergized under usual synchronized operating conditions. The follow-up and resynchronizing relays in Fig. 5 of course retain their energized and deenergized conditions respectively being independent of the three aforementioned ground returns. The same result would obtain if the instructor had operated the synchronization fail switch Z2 so as to disconnect it from line 2l in Fig` 4. Referring to Fig. l and considering the three SR servos simultaneously, the iTOGGLE inputs remain grounded as before, whereas the -ANS, -i-AS, -l-RPMm and AN inputs are grounded respectively through the NC contacts l, 2 and 5 of the respective master lever relays, now denergized.- The short-circuit paths for the control windings are completed through the NC contacts 4 of respective deenergized master lever relays. As a resu-lt the speeder rack servos are frozen in the positions attained just before throwing switch 14 to its offposition.

Referring to Fig. 2- and considering the three toggle servos simultaneously, the CAL and iTOGGLE inputs remain grounded as before, whereas the ANS, -l-RPMm and SR inputs are now grounded through respective NC contacts of the new deenergized automatic relay. The short-circuit paths for the control windings remain complete, so that the toggle servos remain frozen in the undeected zero position.

Referring to Fig. 3 and considering the two band limit servos simultaneously, the ANS inputs of course remain permanently connected to respective main band limit servo answer returns. The -l-RPMma, AN and MaENG inputs are grounded through respective NC contacts of the now deenergized synchronizing relay 30. The short circuit paths for the control windings are now completed through respective NC contacts of the now deenergized synchronizing relay 30, so that the band limit servos are now frozen in the undeflected zero position.

Toggling of the No. 3 engine subsequent to shifting of the synchronizing switch 14 to the oli-position may be considered as typical for the other engine systems were they toggled, having regard to corresponding reference numerals in the systems of the other engines. Minor differences in the operation of the other two engine systems will be pointed out. Assuming that the servo rnotor 3006 had been frozen at a position corresponding to 2400 r.p.m. upon shifting of the synchronization switch 14, let it be assumed that the student pilot desires to decrease the Engine No. 3 speed to say Z300 r.p.rn. To this end he positions the toggle lever 3042 in the decrease position thereby switching the toggle contact 3076 and the TOGGLE. input of the SRS servo from ground to the voltage E and also switching the toggle contact 3088 to open short circuit for the control winding 30M. Conversely if the pilot desired to increase the speed of the No. 3 engine to say 2500 r.p.m. he would position the toggle lever 3042 to the increase position resulting in application of the voltage +B to the :LTOG-GLE input and also resulting in opening the short circuit for the control winding 35H6. inasmuch as the increase operation in analogous to the decrease operation except for reversal in sign of voltage and direction of rotation of the servo motor, the increase operation will be readily understood from the description of the decrease operation and will therefore not be specifically described.

Responsive to application of the input voltage E to the TOGGLE input and, inasmuch as the other inputs, of the SR3` servo are grounded,` responsive only to such input voltage the servo motor moves towards the 2300 r.p.m. position as indicated by the instrument 3032. The slider 3080 also moves towards a new position, corresponding to a deflection of the AN3 servo of +100 rpm. from its undeilected zero position responsive to the toggling operation as will be seen immediately hereinafter, but this is of no `consequence at the present as the ANa input remains grounded. The other speeder rack servos SR2 and SR4 remain frozen in the 2400 rpm. position as their control windings are short-circuited and as their effective inputs including the TOGGLE inputs and the +AS inputs remain grounded, the former through the respective toggle contacts and the latter through the sliders 2320 and 4320 respectively which sliders are in the grounded undeilected zero position of their respective band limit servos. The band limit servos remain in the condition attained when switch t4 was thrown to the center olf-position, i.e. frozen in the undeflected zero position. The conditions of the band limit servos and therefore the three -l-AS inputs are the saine whichever engine is toggled. If the SR2 servo had been toggled Whereas the SR3 and S124 servos had not been toggled, the SR2 servo would `be caused to approach the 2300 r.p.m. position whereas the other speeder rack servos would remain at their 2400 r.p\.n1. positions. Similarly if the SR4 servo had been toggled, the SR4 servo would be caused to approach the 2300 r.p.m. position whereas the other speeder rack servos would remain at their 2400 r.p.m. positions. In other Words during sync. off-toggling each engine behaves as though it were a slave engine.

Reverting to the example of toggling the No. 3 engine, and referring to Fig. 2, with the switching of toggle lever 3042 from its center oft-position, the voltage -I-E is applied to the iTOGGLE input of the AN3 servo through toggle contact 3108 and at the same time the short circuit for winding 3098 is opened with the toggle contact 31116 in the decrease position. Conversely had the toggle lever 3042 `been shifted to the increase position the reference voltage E would have been applied to the iTOGGLE input through contact lM08 and the shortcircuit path for winding 3098 would likewise have been opened. Application of the voltage E merely results in equal but opposite servo motor motion and therefore need not be described in detail. Inasmuch as the other inputs of the AN3 servo are grounded the input voltage -l-E is the only effective input voltage to the servo amplier and as a result the servo motor moves to approach a position of rpm. corresponding to the difference in engine speed between the initial 2400 r.p.m. and the desired 2300 rpm. The other toggle servos remain frozen in their undeflected zero positions. When the student pilot observes an indication by the instrument 3032 of 2300 r.p.m. he reverts the toggle switch 3042 to its center off-position grounding the iTGGGLE inputs to the SR3 and AN3 servos once more through toggle contacts 3076 and 3108 and at the same time closing the short-circuit paths for the respective control windings through toggle contacts 3038 and 3116. All the inputs to these two servos are grounded once more and the servo motors are frozen in the positions corresponding to 2300 r.p.m. and +1100 rpm. respectively. The sync. offtoggling operation so far would have been the same for one of the other two engines had such one engine rather than the No. 3 engine been toggled.

lf the student pilot now repositions the synchronization switch in one of its on-positions, the further events are somewhat ditferent for the case of initial sync. offtoggling of what is now the master engine from the case of snyc. oif-toggling of either of the two engines now slave engines. The further events for either of the slave engines are similar to one another. However, the treatment of the several engine systems can be generalized by the following three equations, in each of which the left hand terrn represents the position of a servo and the terms Von the right hand sies'represent external inputs to such servo:

For one, the servo motor must be free to move to the position indicated by the equation. Inasmuch as the AN servos are generally frozen in place while the other servos may be free to move, these equations should not be solved simultaneously. As a matter of fact it will be recalled, that the toggling servos of the non-toggled engines had been frozen at undeected zero prior to switching of the synchronization switch 14 to the offposition, during toggling, upon completion of toggling, and upon repositioning of switch 14 to an on-position. This is so because the toggle lever and relay contacts that complete the short-circuit paths for their control windings, experienced no change in state, except possibly for the contacts of the master engine relay 17. Had the No. 2 engine been initially or finally the master engine, the short-circuit paths for windings 3096 and 2096 would have opened due to shift of respective contacts 12 and 13 of relay 17, but only momentarily so in vievv'of the in i-mediate closure of an alternative short-circuit path, insufficient to cause motor movement. Except for opening of the short-circuit path of a toggled AN servo during toggling resulting in its deflection of +100 r.p.m., the aforegoing frozen state of its servo motor is likewise true, so that Equation 2 will not apply at all at this point, nor even for the case of sync. on-toggling. It will become effective with operation of the resynchronizing button 34 as described under the heading Resynchronizationf.

Another precaution relates to the value of the term AS in Equations 1 and 3. For reasons apparent hereinafter, the absolute value of the term AS in Equation 1 never exceeds 80 r.p.m., even though the absolute value of the same term AS in Equation 3 may exceed 80 r.p.m.

The series of events subsequent to repositioning switch 14 to an on-po-sition will be covered by a detailed description of the servois operation for one possible combination of toggled and non-toggled engines in each of the two cases of initial toggling of an engine which upon such repositioning became a master engine and of an engine which was or became a slave engine. For other possible combinations the operation is entirely analogous and may be readily determined by reference to the following tables and correspondence of reference numerals.

Table 1.-Master engine initially ioggled Master Slave Slave Engine Engine Engine Table 1I.-Slave engine initially toggled Toggled Slave Engine Non- Toggled Slave Engine Master Engine In each of Tables I `and II combinations are presented in rows and the engines whose servos operate analogously are listed in columns. The rst-listed combination in each table will be described in detail as to operation. Differences as to other combinations arise out of the energization of master engine relay 17 with selection of the No. 2 engine as master engine and the consequent inversion of relations of the No. 2 and No. 3 engines and also out of absence of contacts of this relay at corresponding circuit locations for the No. 4 engine. These can be recognized practically by inspection.

It should be noted that the identity of the master engine prior to switching the synchronization switch ot is immaterial. What matters is the identity of the master engine upon repositioning switch 14 to an on-position. Therefore, for example, for the case where the No.3 engine had been initially the master engine and had there- Y after been sync. off-toggled and thereafter the No. 2 engine had been selected as master engine, the second combination in Table I applies. Considering the first combination in Table l, assuming that the No. 3 engine had been toggled to a 2300 r.p.m. position and that thereafter the synchronizing switch 14 was positioned to the No. 3 position, the input of each of the Speeder rack servos, each of the toggle servos and each of the band limit servos will be reconnected as under usual synchronized operating conditions but the magnitude of some of these input signals will have changed from the initial values corresponding to the 2400 r.p.m. position of the SR3 Servo. The input voltage +VRPM,ma will be reapplied to the +RPMma input through the NO contact 2 of the master lever relay 3044 at its initial value of 240-0 r.p.m. as the master r.p.m. control lever 12 had not been shifted from its 2400 r.p.m. position. However the servo does not revert to its 2400 r.p.m. position as the difference of r.p.m. is now balanced by the input signal to the -AN3 input through the NO contact 3 of the reenergized master lever relay 3044 from the sul-ider 3080 which is now positioned at a position of +100 r.p.m. in accordance with the new +100 r.p.m. position of the AN?I servo attained during toggling and maintained thereafter as previously explained.

As will be seen hereinafter the AS2 or 3 servo is caused to move to a 100 r.p.m. position, but this is of no consequence insofar as the Speeder rack servo of the toggled master engine is concerned as its AS input is grounded through a contact of master engine relay 17. Upon repositioning of switch 14 to the No. 3 position the `+AS3 input of the SR3 servo remains grounded through the NC contact 2 of relay 17. The position of the SRS servo is determined by substitution in Equation l, namely frozen at +100 r.p.m. and the slave engine servos re` mained frozen at 0 r.p.m.

With the repositioning of the synchronizing switch 14 in lits No. 3 oil-position the short-circuit paths for the control windings of the band limit servos are opened once more due to the reenergization of synchronizing relay 30, rendering the respective servo motors free to move again. Considering both servos simultaneously by specie reference toV the ASB o, 3 servo only, the input +RPMma is reconnected to the voltage hI-VRpMma through the NO contact lg of the reenergized synchronizing relay 30. However, the voltage +VRPMma still corresponds to the value of 2400 r.p.m. whereas the input Voltage -MaENG now receives an input corresponding to only 2300 r.p.m., it being reconnected to the slider 3130 of the potentiometer card- 3132, which slider is "27 now positioned in a 2300 r.p.m. position in accordance with the new 2300 r.p.m. position of the RPM No. 3 servo.' The RPM No. 3 servo was positioned at 2300 r.p.m. in accordance with the operation of the SR3 servo. The -AN2 o, 3 input is reconnected through the NO contact of the reenergized synchronizing relay 30 to the slid-er 2134 of the AN2 potentiometer 2136; however this slider remained in lthe undeflected zero position as previously explained. By substituting in Equation 3 there is obtained for the position of the AS2 or 3 (and also previously stated.

Referring again to Fig. l and considering the description of operation of the SR2 servo as also applying to the SR4 servo by implication, its TOGGLE and -AN2 inputs will remain at zero in view of the unchanged position of the toggle lever 2042 and in view of the fact that the AN2 servo has remained in its undeected zero position. The AN2 input is reconnected to the slider 2080' through the NO contact 3 of Ithe master lever relay 2044. The input +RPMmais reconnected to the voltage +VRPMm through the NO contact 2 of master lever relay 2044 at its initial value correspo-r-iding to 2400 r.p.m. The -ANS signal is reconnected to its answer return through the NO contact l of the master lever relay 2044. The +AS2 input remains connected to the slider 2320 of the A82 or 3 card 2322. The AS2 3 servo has assumed a position of -100 r.p.m. as stated but the card 2322 is so contoured as to permit a deviation of the slider 2320 from the undeliected zero position of only i8() r.p.m. The slider 2320 will thereforehave deviated only -80 r.p.m. and the SR2 and SR4 servos will assume a position computed according to the Equation l with the 80 r.p.m limitation inserted: +2400+080=2320 r.p.m. Thus the SR2 and SR4 slave engine servos will run to a final position corresponding to only 2320 r.p.m. and not to the 2300 r.p.m.v to which the master engine speeder rack servo had been toggled. Had :the master engine Speeder rack servo been toggled from an initial 2400 r.p.m. to a final speed no less than 2320 r.p.m., the SR2 servo (and for that matter the SR4 servo) would have followed the SRS yservo to synchronism. The slave engines may now be resynchronized individually by operating their respective toggle levers or concurrently by operating the resynchronizing button 34; these two modes of resynchronization will be discussed hereinafter under the headings Sync. On-Toggling and Resynchronization.

Referring to Fig. 2, owing to the movement of the slave Speeder rack servos the SR inputs to the slave engine toggle servos are changed accordingly to a value corresponding to 2320 r.p.m. or whatever final position assumed by the slave Speeder rack servos, but this is of no further consequence as the respective control windings remain short-circuited. Their remaining inputs are supplied as under the initial usual synchronized operating conditions with the master r.p.m. control i2 positioned to a selected speed of 2400 r.p.m., whereas all of the inputs of the toggled master engine toggle servo (AN2) are grounded as under the initial usual snychronized operating conditions.

Considering the case of initial sync. ofi-toggling of a slave engine, specifically the tirst combination in Table 1I, at the end of the toggling operation andbefore repositioning of the synchronization switch 14, the No. 3 and No. 4 servos were in the same condition as upon switching of the synchronization switch 14 to its otiposition, Vthese servos not having been toggled. The AS2 or 3 servo in this example is associated with the No. 2 engine as the slave engine. Upon repositioning of the synchronization switch in the No. 3 position, the No. 3 and No. 4 servo systems revert to their usual synchronized operating conditions corresponding. to the selected speed of.2400 r.pm. By analogy to the previous example 28 with reference to the toggling of the No. 3 engine, at the end of the toggling the SR2 servo had assumed a position corresponding -to 2300 r.p.m., its control winding was short-circuited and all its effective inputs were grounded. The AN2 servo had assumed a position corresponding to +100 r.p.m., its control winding 2098 was short-circuited and each of its external effective inputs -f-RPMma, SR2 and iTOGGLE were grounded. The AS2 o, 3 servo had its control winding 2332 short-circuited in the undeected zero position, while each of its eiective external inputs +RPMm, -AN2 0,3 and MaENG were grounded. With the repositioning of the synchronization switch 14 the winding 2098 of the AN2 servo remains short-circuited at the +100 r.p.m. position, whereas the short-circuits for the windings of fthe SR2 servo and the AS2 or 3 servo are opened again due to the reenergization of the master lever relay 2044 and of the synchronizing relay 30 respectively. These servos had then become free to move again. The AS2 or 3 servo assurnes a position computed according to Equation 3:

The SR2 servo assumes a position according to its effective input signals y-l-S2, +RlE'Mma and -AN2, except that the +AS2 input has not assumed the value of +100 r.p.m., but a value of only r.p.m. as limited by the contour of the AS2 or 2 potentiometer card 232,2. By substitution in Equation l SR2=2380 r.p.m. and the SR2 servo assumes such position. If it is desired to return the No. 2 engine to the synchronous speed of 2400 r.p.m. it would be necessary to toggle the No. 2 engine or -to depress the resyuchronizing button These operations will be explained under the headings Sync On-Toggling and Resynchronizationf The AN2 servo is of course reconnected as under usual synchronized operating conditions. lts SR2 input however corresponds to only 2380 r.p.m. in accordance with the new position of the toggled slave engine (SR2) servo. This is of no consequence at the present, as the control winding 2093 remains short-circuited.

SYNC. ON-TOGGLING As in the case of sync. oi-toggling the description except for reversal of signs of voltages and directions of servo motor rotation applies equally to toggling for increase and decrease of the engine speed. The descrip tion will be limited again to the case of decreasing the engine speed, say from 2400 r.p.m. to 2300 r.p.m. Again the cases of master engine and slave engine toggling must be diierentiated; Tables and II should be referred to again, as only the first-listed combinations therein will be described. The initial conditions prevailing in this example are the usual synchronized operating conditions.

Equations 1 and 3 are applicable again upon mpletion of toggling to all engines and are applicable even during ltoggling to the non-toggled engines. Equation 2 still has no application for the non-toggled systems during or after toggling; for the toggled engine during actual toggling it is best to consider the Speeder rack and toggle servomotors as moving under the iniiuence of the voltages 1n and iE respectively and in a manner more nearly similar to a continuously operative motor rather than a servo positioning motor; the motors are brought to a stop by repositioning of the associated toggle lever to the center-oli position. The upper and lower signs for the voltages 1E and t-E correspond 1to toggling to decrease and increase engine speed respectively. (Equation 2 becomes elective upon resynchronization as discussed hereinafter.

The sole influence of the toggle voltage :rE holds exactly true in the case of the toggled Speeder rack servo, as its inputs other than the TOGGLE input are grounded through respective NC contacts of the associated master lever relay (Fig. l), which is deenergized with operation of the associated toggle lever (Fig. 4). On the other hand, the associated toggle servo (AN) receives effective Y external signals to the +RPM,ma `and -SR inputs over respective NC contacts of the master lever relay and respective NO contacts of the synchronizing relay 30 in the form of the voltage +VRpMma and of the voltage derived from the associated speeder rack servo card respectively (Fig. 2).

However the iTOGGLE summing resistor 3079 is so pro-positioned with reference to the +RPMum summing resistor 3081 and the -SR3 summing resistor 3083 of the AN3 servo as to render the +RPMma and -SR3 inputs negligible in comparison with the iE toggle voltage. The same considerations prevail yfor the AN2 and AN4 servos as recognized by correspondence of reference numerals.

Considering the case of sync. on-toggling of a master engine and more specifically Ithe rst-listed combination in Fig. 1, with the toggle lever 3042 positioned in the decrease position, the master lever relay 3044 is deenergized so that the -ANS, +RPMma and -AN3 inputs of the SR3 servo (Fig. l) are grounded respectively through the NC contacts l, and I of the master lever relay 3044. The +AS3 input remains grounded through the NC contact g of the master engine relay 17. With the deenergization of the master lever relay 3044 its NC contact in the short-circuit path for winding 3016 is closed, but the short circuit remains incomplete due tov the shifting of the toggle contact 3088. As a result the SR3 servo continues to remain free to move but in accordance with the input signal -E only. The servo motor moves and the extent of movement is noted by the student pilot at the indicator 3032. When the indicator 3032 registers 2300 r.p.m. the student pilot repositions the toggle lever 3042 to its center-off position reenergizing the master lever relay 3044 so that the SR3 servo continues to remain free to move while it is now subject to the external inputs +RPMma at the initial 2400 r.p.m., and -AN3, now, as will be seen at -100 r.p.m., holding the SR3 servo in the 2300 r.p.m. position in accordance with Equation 1.

Referring to Fig. 2, While the toggle lever 3042 had been placed in its decrease position, the short-circuit path for the AN3 servo was opened due to the opening of the toggle contact 3116 so that the AN3 servo moved substantially solely under the influence of the toggle vol-tage +E, the effect of the external signals to inputs +RPMma and -S'R3 being negligible as explained. At the completion of toggling the AN3 servo motor had moved to and was frozen in a +100 r.p.m. position as under sync. offtoggling. The external inputs +RPMma and SR3 and the i-TOGGLE input are grounded once more as under usual synchronized operating conditions.

Referring to Fig. 3 and considering the two band limit servos concurrently, even though in accordance with the previous practice only the AS2 or 3 servo operation is described expressly, its +VRPMma input remained at 2400 r.p.m. as before toggling, whereas its -AN2 or 3 input remained at zero, the AN2 engine having remained at the undeected zero. On the other hand its -MaENG input had changed from 2400 r.p.m. to 2300 r.p.m., so that the AS2 o, 3 servo deects to -100 r.p.m. in accordance with Equation 3. Referring again to Fig. l and again considering the operation of the SR2 servo as typical also of the SR4 servo, the SR2 servo is now subject to effective signal inputs of +AS2 and +RPMma. The -AN input remains at zero as the AN2 servo remains in its undeected zero position. In view of the aforesaid limitations introduced by the contour of the potentiometer 2322, the +AS2 input has not assumed a value of -100 r.p.m. but only of -80 r.p.m. so that the SR2 servo assumes a final position of 2320 r.p.m. in accordance with Equation l. 'Ihe two slave engine systems may be resynchronized individually by individual sync. ontoggling as described immediately hereinafter or conso s currently as described under the heading Resynchronz tion.

Considering the case of sync. on-toggling of a slave engine and more specilically the rst combination in Table II: referring to Fig. l and again assuming initially usual synchronized operating conditions at 2400 r.p.m.,

with the shifting of the toggle lever 2042 to thedecrease position the SR2 servo and the AN2 servo will behave much in the same manner as did the SR1, servo and the AN3 servo in the previous example in view of the fact that all but the iTOGGLE input to the SR2 servo are grounded. However the AN2 servo with the release of the master lever relay 2044 attendant to toggling4 has its -ANS input still connected to the answer return `but now through the NC contact 5 of the master lever relay 2044 and line 2106. Its +RPMmavinput remains returned to the voltage +VRPMma equivalent to 2400 r.p.m., but now through the NC contact f of the master lever relay 2044. The SR2 input remains returned to the slider 2112 of the speeder rack potentiometer 2114 but now through the NC contact v7 of master lever relay 2044 and line 2110. The AN2 servo therefore remains subject to the input signals +RPMma and -SR2, but these input signals are negligible in comparison to the voltage +B applied to the iTOGGLE input through the toggle contact 2108. The AN2 servo with repositioning of the toggle lever 2042 in the off-position arrives at a position corresponding to r.p.m. Referring to Fig. 3, the AS4 servo remains at undeflected zero in accordance with Equation 3, as the -AN4 servo input remains at zero and the +RPMma and Mal-ENG inputs remain at 2400 and 2400 r.p.m. respectively. On the other hand the AS2 r 3 servo deflects to -100 r.p.m., for although its +RPMma and MaENG inputs yalso remain at +2400 and 2400 r.p.m. respectively, its AN2 input has now assumed a value corresponding to -100 r.p.m. When the toggle lever 2042 is restored to its center-olf position, the No. 3 and No. 4 engine systems remain unalected, the AN2 servo is frozen at the position corresponding to +100 r.p.m., and the AS2 or 3 servo remains at the position corresponding to +100 r.p.m. as its -AN2 or 3 input remains fixed at +100 r.p.m. In accordance with Equation 1 the SR2 servo will reposition itself according to the signals +RPMma (2400 r.p.m.), -AN2 (-100 r.p.m.) +AS2. However +AS2 is limited to +80 r.p.m. and does not attain the +100 r.p.m. of the AS2 or 3 servo for reasons previously stated, so that the iinal position of the SR2 servo will be 2380 r.p.m.v Had this servo been toggled to no less than 2320 r.p.m. it would have reverted to synchronism. To restore synchronism the No. 2 engine may be toggled with synchronization on in the manner above described, or it may be resynchronized as described immediately hereinafter.

RESYNCHRONIZATION The starting point for the resynchronization operation presupposes that one lor both slave engines are out of synchronism with the master engine, say at 2320 r.p.m. or 2380 r.p.m. whereas the master engine is at 2300 r.p.m. or 2400 r.p.m., these effects being dueto toggling as described in the examples under sync. offJtoggling and sync. on-toggling. The circuit conditions may be assumed to be the same as at the end of sync. on-toggliug of the master engine (the first combination of Table I which will be specifically described). Under this assumption the No. 2 and No. 4 engine servo systems will operate in analogous manner concurrently; except for the initial speed of 2320 r.p.m. and the final speed of 2300 r.p.m. as opposed to an initial speed of 2380 r.p.m. and a nal speed of 2400 r.p.m. and also except for some possible sign reversals in the r.p.m. values, the description applies to the first combination of Table II as Well, but only insofar as the No. 2 engine is concerned, as the No. 4 engine system in such case had been in synchronism throughout 

